What Milsim providers are there beside Warzone, tier 1 and Sterling? They're the kind of thing I'm after but I'd rather something woodland instead of FIBUA sites everyone seems to be using
Gunman does a range of 'filmsim' games. These include vietnam, WW2, Cold war and modern. I have done a couple of the WW2 ones and they have been excellent fun. I wouldn't really compare them to milsim, but definitely a step up from an open day.
Okto 8 is very much a social event with two 8 hour games in between. I would not recommended it as a hard core Milsim but I would still recommend going as it is something different and on the whole the players are great.
Airbounre typically only play one day as a Milsim event followed by a skirmish the following day but that isnt always the case sometimes it just the one day.